The present state of the art in pair-feeding of animals for testing and experimental purposes involves a delayed feeding system using liquid diets delivered from Richter tubes. A Richter tube is an elongate tube having a series of graduations for measuring the amount of liquid in the tube. At the lower end of the Richter tube is a U-shaped delivery tube from which an animal may withdraw liquid food. An air pocket above the liquid normally retains the liquid in the elongate tube and U-shaped delivery tube.
While the Richter tube has been used in animal feeding experiments for several years, it does not guarantee simultaneous feeding of two or more animals used in an experiment. During animal feeding experiments, it is customary to feed one animal a liquid which may adversely effect the health of that animal and to feed another animal a control liquid having no known adverse health effects. For example, experiments conducted to determine the adverse effects of alcohol normally involve feeding one rodent a liquid including alcohol and a second rodent a control liquid, each liquid being equivalent in caloric value. The problem with these experiments, however, is that the animal may have a natural aversion to or preference for one of the two liquids. For example, rodents are known to have a natural aversion to alcohol. While liquid diets incorporating alcohol have been developed to overcome the rodents natural aversion to alcohol, the rodent will consume the alcohol liquid diet only to avoid starvation. On the other hand, the rodent consuming the control liquid will feed at a rate to satisfy its hunger. To ensure that the tested rodent and control rodent receive liquid of equivalent caloric value in a given time period, both rodents are supplied an amount of liquid equivalent to that which the rodent on the alcohol diet would be expected to consume during that same time period. As a result, the control animal tends to consume all of its liquid in the early stages of the time period while the experimental rodent consumes its liquid at a substantially steady rate over the entire time period. This is known as a delayed feeding system because the control animal receives an amount of diet equivalent to that consumed the previous day by the animal fed the alcohol containing diet. The result is that the nutritional and hormonal status of the control animal and the alcohol fed animal vary markedly at different times of the day. It is quite conceivable that some of the effects to alcohol consumption may actually result from differences in the nutritional patterns of the animals. The effects of nutritional patterns may be substantial since these experiments are usually performed over several weeks. Accordingly, the results of the testing and experimentation may not be conclusive. This problem is further enhanced when more then two animals are used in an experiment where there is one control liquid diet and several testing liquid diets containing various products to which the animals may have various degrees of preference.